Nearly all fission reactions utilizing the uranium isotope, U.sub.235, require a concentration of the U.sub.235 isotope greater than in the naturally occurring state. The process of enrichment whereby the concentration of U.sub.235 in natural or depleted uranium is raised to a desired level has been achieved in the past by many techniques which generally operate to separate U.sub.235 from the other uranium isotopes, chiefly U.sub.238, on the basis of its slight chemical or mass difference. Enrichment according to these techniques often requires cascaded processing using a sequence of repeated applications of the same steps, each step providing a slight increase in the concentration of the desired U.sub.235 isotope.
A promising new technique for efficient isotope enrichment operates by exposing a vapor of uranium to pulsed laser radiation to produce a plasma of selectively ionized U.sub.235 atoms and to permit separation of U.sub.235 ions based on their electrical charge. Typically, separation of the ions resulting from selective ionization is achieved by accelerating them out of the vapor toward a collecting surface through pulsed application of crossed-field MHD acceleration forces to the plasma just after its creation with each pulse of laser radiation. In using this process, it has been noted that the plasma, a conducting medium, has associated with it a skin depth effect which impedes the penetration and correspondingly the effectiveness of the electrical field component of the crossed-field MHD acceleration force. Additionally, the electrons in the plasma being of much lower mass and more easily accelerated, will contribute a substantial electron current distinct from the ion current of desired U.sub.235 atoms. The large electron current may result in electrode degradation and will lead to the generation of substantial Hall voltages which permitted to short circuit will impair the enrichment process efficiency.